Embodiments of the present invention relate to thin film batteries and their fabrication and packaging.
Thin film batteries are used in applications that require a small battery with a high energy density such as, for example, portable electronics, medical devices and space systems. A typical thin film battery typically comprises a substrate having one or more battery component films which cooperate to store electrical charge and generate a voltage. The battery component films include an electrolyte sandwiched between electrode films. The battery component films are thinner than conventional batteries, for example, the films can have thicknesses of less than 1000 microns, or even 100 microns. This allows thin film batteries to have thicknesses which are much smaller than the thickness of conventional batteries. The battery component films are often formed by processes such as physical and chemical vapor deposition (PVD or CVD), oxidation, nitridation, and electroplating processes. These batteries can either be used individually or stacked together to provide more power or more energy.
A polymer bead around the edge of a battery cell has been used to package thin film batteries by enclosing and sealing off the battery cells to reduce or prevent degradation of battery component films in the environment. The battery component films can chemically react with moisture, gases such as oxygen, nitrogen, carbon monoxide, and carbon dioxide, and even organic compounds and solvents present in the atmosphere. The polymer bead provides good packaging for thin film batteries as they can be shaped in a softened or viscous state at elevated temperatures to form good seals and are relatively lightweight.
However, although thermoplastic polymers can provide good oxidation resistance and can be suitable for packaging, thermoplastic materials have not been extensively used in packaging of batteries as they were found to thermally degrade during processing of the battery packaging. For example, most thermoplastics are degraded by temperatures of 100 to 120° C., which are the operating temperatures for laminating machines. Further, it is difficult to form a sealing package made from thermoplastic material around a battery without causing thermal degradation of the battery component films or other structures of the battery. This is because conventional laminator machines and related packaging methods can expose the active area of the battery cells themselves to elevated temperatures causing degradation in the quality of the battery cells, and resulting in substantial losses in open circuit voltage and degraded shelf-life of the cells.
For reasons including these and other deficiencies, and despite the development of various packaging methods for thin film batteries, further improvements in battery packaging and their methods of fabrication are continuously being sought.